<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            height: 200px;
            width: 200px;
            float: left;
            /* float (left or right)鼠标往左或后移动 */
        }
        #No1{
            background-color: red;
            
        }
        #No2{
            background-color: blue;
            
        }
        #No3{
            background-color: green;
            
        }
        p{
            clear: both;
            /* clear(both or left or right) 清除浮动标签 */
        }
    </style>
</head>
<body>
    <div id="No1">123123</div>
    <div id="No2">123123</div>
    <div id="No3">123123</div>
    <p>111111</p>
</body>
</html>